Thermoelectric properties of new Zintl phases: Ba/sub 4/In/sub 8/Sb/sub 16/ and Ba/sub 6/Ge/sub 25-x/

A new compound Ba/sub 4/In/sub 8/Sb/sub 16/ is being explored for thermoelectric potential. It crystallizes in the orthorhombic space group Pnma with a=10.166(3) /spl Aring/, b=4.5239(14) /spl Aring/, c=19.495(6) /spl Aring/, and Z=1. Ba/sub 4/In/sub 8/Sb/sub 16/ has a 2-dimensional structure with thick corrugated (In/sub 8/Sb/sub 16/)/sup 8$/layers separated by Ba ions. The compound is a narrow band-gap (/spl sim/0.10 eV) semiconductor. Polycrystalline ingots of Ba/sub 4/In/sub 8/Sb/sub 16/ show room temperature electrical conductivity of 135 S/cm and a Seebeck coefficient of 70 /spl mu/V/K. The thermal conductivity of Ba/sub 4/Ln/sub 8/Sb/sub 16/ is about 1.7 W/m/spl middot/K in the temperature range of 150-300 K. The new compound Ba/sub 6/Ge/sub 25-x/ was also examined. Ba/sub 6/Ge/sub 25-x/ adopts chiral clathrate structure with cubic space group P4/sub 1/32 and dimension of a=14.5483(2) /spl Aring/. Ba/sub 6/Ge/sub 25-x/ shows room temperature electrical conductivity of 2000 S/cm and a Seebeck coefficient of -18 /spl mu/V/K. The thermal conductivity was about 2.5 W/m/spl middot/K at room temperature. Both of the compounds reported here are air and moisture stable.